#include<iostream>
class Nguoi
{
public:
	virtual void Chao();
};
virtual void Nguoi::Chao(){
	cout << "Toi chua biet chao";
};
class NguoiViet :public Nguoi
{
    public:
	void Chao();
};
class NguoiAnh :public Nguoi{
public:
	void Chao(){
		cout << "Hello";
	}
};